Various forms of inductive sensor have been used to generate signals indicative of the position of two relatively movable members. Typically, one member carries an excitation winding and two or more sensor windings while the other member carries a resonant circuit. The magnetic coupling between the resonant circuit and each of the sensor windings varies with position so that, by applying an oscillating signal at the resonant frequency of the resonant circuit to the excitation winding, a signal is induced in each of the sensor windings which oscillates at the resonant frequency but whose amplitude varies as a function of the relative position of the two members.
International Patent Publication WO 94/25829 describes a rotary position sensor in which two excitation windings and a sensor winding are orthogonally positioned about a rotating element which includes a resonant circuit such that the magnetic coupling between each of the excitation windings and the sensor winding varies in accordance with the angular position of the rotating element. An in-phase oscillating signal and a quadrature oscillating signal (that is 90° out of phase with the in-phase oscillating signal) are respectively applied to the two excitation windings and the rotary position of the rotating element is determined from the relative amplitudes of the components of the signal induced in the sensor winding corresponding to the in-phase signal and the quadrature signal.
A problem with the rotary position sensor described in WO 94/25829 is that the processing required to derive the rotary position from the signal induced in the sensor winding is not well suited to digital processing techniques.